The present invention relates to absorbent articles.
A various assortment of absorbent articles of the disposable type, such as diapers and sanitary pads, have been proposed which are discarded after a single use. Several factors are of importance in determining whether such articles will be acceptable to the consumer. The articles should rapidly receive and dissipate body fluids without a significant amount of backwetting to the wearer's skin, and should be available to the consumer at a relatively low cost, since they are not reused.
Much of the cost and deficienceis in prior articles may be attributed to the structure of and the materials used in the articles. In the case of disposable diapers, structures are often provided having an absorbent pad, a fluid impervious backing sheet covering a back surface of the pad, and a fluid pervious top sheet covering a front surface of the pad. Particularly in the case where the absorbent pads are made of a mass of fibers, such as comminuted wood pulp known in the art as fluff, an absorbent wadding sheet is often placed over the front surface of the pad to prevent balling and maintain structural integrity of the pad during use. In addition to adding to the cost of the diapers, such top wadding sheets impair the function of the diaper in a number of respects. The wadding sheets impede the rapdity of fluid passage from the top sheet into the pad, and retain fluid adjacent the front surface of the diaper, thus increasng the amount of backwetting from the diaper to the infant. The wadding sheet also adds stiffness to the diaper, thus decreasing the amount of comfort the diaper provides for the infant. In addition to lacking structural integrity, the fibers in the fluff pads collapse when wetted and placed under loads, thus decreasing the absorbent capacity of the pads.
As indicated above, many of the absorbent pads are currently made from wood fluff which is normally formed by fiberizing or comminuting pulp board. The pulp board itself is normally formed from trees through a pulping process. The pulping processes may be categorized as chemical, semichemical, mechanical, and thermomechanical. All of the wood fluff used in absorbent articles sold in the United States known to the applicant has been exclusively formed from a chemically produced pulp. For a given species of wood, the chemical pulping process produces a pulp having fibers with a longer length than the fibers produced by the other pulping processes, particularly the mechanical pulping process. Accordingly, the industry has sought chemically produced pulp for use in disposable pads since the long fibers enhance the structural integrity and loft of the pad.
In spite that the chemical pulp results in a pad with desirable characteristics, a number of disadvantages are inherent in the use of such pulp. First, the chemical pulping process is relatively inefficient in that the yield of pulp to the amount of wood used in pulping is in the range of 40 to 55%, whereas the yield of the mechanical and thermomechanical pulping processes is as high as 90-95%. The disparity in yields between the processes is due to the removal of lignin, cellulose, and hemicellulose from the wood during digestion in the chamical procedure. Accordingly, chemically produced pulps are significantly higher in cost than mechanical and thermomechanical pulps, necessarily resulting in a more costly item to the consumer. Also, the vital raw materials are not used to the desired extent in chemical pulps, thus detracting from our natural resources.
Second, environmental considerations favor the use of pulps which are not produced by the chemical process. In the chemical sulfite process, it is relatively difficult to reclaim the cooking chemicals used during pulping. Hence, the manufacturer must dispose of the chemicals, and it is believed that more than one sulfite processing plant has been closed due to contamination of water by the chemicals, which the Environmental Protection Agency considers dangerous. Although it is less difficult to reclaim the chemicals used in chemical kraft pulping, this process is characterized by the emission of gases containing malodorous substances, such as mercaptans and organic sulfides, and is also repugnant to the community at large.
Third, the energy required to fiberize pulp board solely of the chemical type is greater than that necessary for a pulp board containing mechanical or thermomechanical produced pulp. This follows since lignin of the fibers is removed during chemical pulping, thus increasing hydrogen bonding between dry fibers of the chemical pulp.
Finally, it is preferred to obtain an absorbent pad which overcomes the above objections, and yet has improved structural integrity and resiliency.